The invention relates to a method for reeling a paper or board web in a drum reel-up or equivalent, in which, when a paper or board reel formed on a reel spool situated in a reeling position in nip-defining relationship with the reel drum becomes complete, a new, empty reel spool is brought by means of transfer members into a stand-by position and accelerated up to the web running speed. The reel spool with the complete reel is transferred by means of a transfer device into an exchange position apart from the reel drum, and the new, empty, initially accelerated reel spool is transferred into the reeling position.
The invention also relates to a device for reeling a paper or board web in a drum reel-up or equivalent, which device comprises a reel drum and a reel spool whereby a paper web is fitted to run through a nip defined between the reel drum and the reel spool and then onto the reel spool. The device comprises a transfer device for bringing a new, empty reel spool into nip-defining relationship with the reel drum after the paper or board reel on the first reel spool is complete.
As is well known in the art, when a web is reeled by means of a drum reel-up or an equivalent reel-up, the web is passed on the face of the mantle of a reel drum, a reeling cylinder or equivalent before the reeling nip, while the web forms a belt angle over the reeling cylinder or equivalent. Problems have arisen from sliding between the web and the reeling cylinder which causes fluctuations in the tension of the web. Further, during replacement of a full reel for a new empty reel spool, fluctuations have occurred in the tension of the web, which in this instance may also result in problems in the paper forming processes preceding the reeling process.
A drum reel-up is used commonly to reel the paper web that comes, for example, from a paper machine, a coating machine, a supercalender and from a printing machine. In a drum reel-up, the web is reeled onto a spool, and the reel that is being formed, i.e., the structure of the web being wound onto the reel spool in combination therewith, is pressed against the reel drum or reeling cylinder, over which the web runs on a certain sector and which is rotated at a circumferential speed that corresponds to the speed of the web. Before completion of the reel, a new, empty spool can be brought into nip-defining relationship with the reel drum so that it also obtains the corresponding circumferential speed. As soon as the reel of paper has obtained the desired diameter, it is transferred apart from the reel drum. Then its speed of rotation starts becoming lower, which has the consequence that, between the new reel spool and the full reel, a web loop is formed. This loop is guided by means of a compressed-air jet to be wound around the new, empty reel spool and is then torn apart from the full reel of paper so that the web starts to wind onto the new, empty reel spool.
It is conventional in drum reel-ups that at the reeling stage, normally the spool of the paper reel rests and revolves on two support rails. To permit this, there are particular bearing parts at ends of the reel spool, which bearing parts also guide the transfer of the reel as it is transferred along the rails to further processing upon completion of the reel. In paper manufacture, this further processing is usually slitting which entails cutting the reel and unwinding it into smaller rolls of paper. The returning and changing of the empty reel spools can be carried out, for example, by means of a crane or other suitable machinery.
When certain paper grades are being reeled, for example LWC and SC paper grades, it is a problem that the paper to be reeled slides on the face of the reeling cylinder especially at higher web running speeds. This sliding problem occurs especially in the reel-ups driven by the circumference described above, i.e., those in which the new replacement paper reel obtains the power required for its rotation from the circumference of a driven reeling cylinder and transfers it to its own circumference through friction force between the paper and the face of the reeling cylinder. When the friction force is lower than a certain limit value, sliding occurs between the face of the reeling cylinder and the paper to be reeled which results in uncontrollable variations in tightness and hardness in the paper reel that is being formed. These variations in tightness and hardness produce unwanted wrinkles in the reels, especially in the inner layers, so that the inner portion of the reel becomes broke. As a result, substantial economic losses are incurred for the paper mill.
The above sliding of the paper against the face of the reeling cylinder depends on the tension of the paper in the area of the reeling cylinder and on the resulting surface pressure against the face of the reeling cylinder. Another factor that affects the sliding is the linear load that is produced by the primary and secondary reeling forks on the growing paper reel against the reeling cylinder. Further, the occurrence of sliding is affected by the surface properties of the paper that is reeled and the reeling cylinder, i.e., the friction coefficient between these surfaces, which is also affected by the humidity of the paper.
An increased tension of the paper increases the tendency of sliding but, on the other hand, it reduces fluttering of the paper. However, the tensile strength of the paper sets an upper limit for an increase in tension vis-a-vis increased breaks in the paper web. Maintaining the linear load between the reel that is being formed and the reeling cylinder sufficiently high and stable is complicated because the reeling is started on primary forks that are in an upper position and is continued on secondary forks in a later stage. The primary forks bring the reel downward to an inclined contact with the face of the reeling cylinder, and the reel begins to receive its rotation power from the circumference of the reeling cylinder. As the reel becomes larger and the primary forks are lowered gradually to their lower position, attempts are made to keep the linear load between the reel and the reeling cylinder invariable despite a reduction in the force component arising from the gravity of earth as the position of the growing reel changes in relation to the reeling cylinder. This takes place by means of separate relief cylinders.
One of the most difficult parts of the control of the linear load is the stage in which the growing reel is transferred from the primary forks to the secondary forks. In practice, in this stage, there are noticeable variations in the linear load, which variations permit momentary sliding of the paper on the face of the reeling cylinder. This results, from time to time, in the above-described wrinkling of the paper in the initial stage of the reeling.
At the reeling stage, for example drum reeling, the transfer from primary forks to secondary forks causes discontinuity in the reeling of the web and, as a result, bottom broke in the paper reel.
The transfer of the reel from primary forks to secondary forks may also cause variations in the tension of the paper, which variations may be a reason for sliding and for wrinkling of the paper.
One of the prior art means for avoiding the above-discussed sliding problem and its consequences is to set the tension of the paper as low as possible by regulating the difference in speed between the reeling cylinder and the nearest drive mechanism preceding it. As stated above, in this connection, a restricting factor is the fluttering of the web and the resulting increased tendency of web breaks and deterioration of the quality properties of the paper, e.g., the formation of folds.
Another procedure used to avoid the sliding problem and its consequences is to increase the linear load between the growing reel and the reeling cylinder to a level as high as possible by using an excessively high loading force on the carrier forks, especially on the secondary forks, with which loading force the reel is pressed against the reeling cylinder. Reduced quality properties of the paper are a drawback in this procedure because the tensile strength and the stretch of the paper are reduced.
With respect to the prior art most closely related to the method and device in accordance with the present invention, reference is made to Finnish Patent Application No. 905284 (corresponding to U.S. Pat. No. 5,251,835 assigned to the same assignee herein and the specification of which is hereby incorporated by reference herein) which describes a method for reeling a web wherein, when the machine roll becomes full, a new empty reel spool is brought by means of transfer members into the stand-by position and accelerated to the web speed. At the same time as the machine roll connected to the center drive is transferred by means of the machine roll transfer device to the exchange position apart from the reel drum, the new pre-accelerated reel spool is lowered onto the rails, and the exchange is carried out in a manner in itself known. Thereafter, the full machine reel is slowed down and the transfer device for the full machine reel is shifted to the new reel spool, and the center drive is connected to the new reel spool. In this method, the web is not supported during the reeling on any surface.
From the prior art, so called WINBELT reel-ups are also known, in which reel-ups a carrier belt which runs between belt rolls is used. One of these belt rolls is usually provided with a drive and the other belt roll is mounted on fastenings. The positions of the belt rolls are substantially stationary, and their position is changed only to the extent that is required to adjust the tension of the belt. By means of this arrangement of belts, attempts are made to provide a difference in speed in relation to the reeling, and by means of this difference in speed, attempts are made to provide optimal linear loads as the reeling progresses.
With the present paper and surface treatment machines, attempts are made to achieve ever higher speeds, so called high-speed reeling, in which reeling the speed is higher than about 1600 meters per minute. High-speed reeling results in increased air resistance and friction, for example, an increase in speed makes the air resistance four-fold, which may lead to problems in the running of the web. While aiming at ever higher web running speeds, attempts are made to use recycled fibres as extensively as possible. However, such recycled fibers are not as strong as virgin fibres. Further, at the same time, attempts are made to provide thinner paper grades, in which case the paper grade that is used is weaker. In such cases, it is important to arrange the reel spool exchange in such a way that there is no discontinuity in the reeling of the web, and at the same time, to more accurately control the reeling parameters.